This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:    3GPP third generation partnership project    AMU antenna management unit    ASIC application specific integrated circuit    BBU baseband unit    CDMA code division multiple access    CPRI common public radio interface    DL downlink (from base station to UE)    DRAN dense RAN    DSP digital signal processor    FDD frequency division duplex    FDM frequency division multiplexing    ID identification    I/F interface    IRC interference rejection combining    LTE long term evolution    LTE-A long term evolution advanced    MAAS multi-antenna aperture selection    Mbps megabits per second    MHz mega-Hertz    MIMO multiple input multiple output    MU multi user    MIPS microprocessor without interlocked pipeline stages    OBSAI open base station architecture initiative    RF radio frequency    RAN radio access network    DRAN dense RAN    RRH remote radio head or remote RF head    SINR signal-to-interference noise ratio    SRS sounding reference signals    TDM time division multiplexing    UE user equipment    UL uplink (from UE to base station)
In places with a very high density of data subscribers in a wireless system, it is difficult for the operator of the system to provide an adequate data rate to each subscriber. For example, in a stadium sporting event, there can be many thousands of spectators. Spectators can be as dense as 1.5 per square meter. Suppose half of the spectators are subscribers to a given wireless service and one percent of those are asking for a download or upload simultaneously. This is admittedly a “peak” scenario but not too extreme. If the users expect a 1 Mbps (megabits per second) data rate, a cell (typically 10 Mbps/cell downlink for 10 MHz FDD-LTE) would be able to support about 200 spectators seated in an area of 133 square meters. Note that 133 square meters is roughly the area of a circle of radius 6.5 m. With cells packed this densely, cell-edge effects become dominant.
Even provided with many low power antennas and corresponding receivers and/or transmitters, a wireless system can be easily overwhelmed by this amount of traffic. Conversely, increasing capacity through additional hardware can be expensive or impossible. It would be beneficial to provide the ability to use currently installed hardware to improve wireless capacity.